Such gear systems are already known from the prior art, for instance Proceedings of Actuator 2000, June 19-21, Bremen, “Pancake shaped micro gear system with high transmission ratio” by R. Degen, W. Ehrfeld, and F. Michel; Das Micro Harmonic Drive der Micromotion GmbH: Ein Präzisionsmikrogetriebe für Positionieraufgaben [Micromotion GmbH's Micro Harmonic Drive: A Precision Micro Gear for Positioning Tasks] by R. Degen and F. Michel, F&M 109 (2001), No. 6, 48-50; and Proceedings of Innovative Klein-und Mikroantriebe [Innovative Miniature and Micro Drive Mechanisms], May 15-16, 2001, Mainz, “Micro Harmonic-Drive: Innovative Antriebstechnik miniaturisiert mit LIGA” [Micro Harmonic Drive: Innovative Drive Technology Miniaturized with LIGA], by R. Degen. Examples of such known micro gear systems on the principle of strain wave gear systems, such as Harmonic Drive (registered trademark), are also shown in FIGS. 2a, b and FIG. 3 and will be described briefly below with respect to the principle of their mode of operation. It will also be noted that the aforementioned published prior art is expressly incorporated by reference into the disclosure content of the present patent application.
The gear principle of a strain wave gear system 56 is distinguished from other designs, such as stationary spur gear systems and planetary gear systems, by its precise and backlash-free transmission properties. These special properties have long been documented in robotics, machine tool design, measuring instruments, air and space travel, and medical technology by the Harmonic Drive principle. Depending on their embodiment, Harmonic Drive gear systems can be classified as either cup gear systems (FIG. 2a) or flat gear systems (FIG. 2b). The flat construction of this gear principle offers major advantages, especially with a view to micro drive systems, such as the low number of components required, a compact design, and the level of transmission ratio that is required for micro motors and that can be attained with a single gear stage. The basic elements of the Harmonic Drive gear system of flat construction are composed of the wave generator 12 and the gear wheels known as the flexible spline 22, circular spline 24 and dynamic spline 26. As can be seen from FIG. 3, the wave generator 12 in Harmonic Drive gear systems of flat construction is preferably formed by a planetary gear system, comprising one central sun wheel 14 and two or more planet wheels 16 which mesh with the teeth of the sun wheel 14 and in turn mesh with the internal teeth of the flexible spline 22.
The fundamental principle of a Harmonic Drive gear system is that the wave generator 12 deforms the flexible spline 22 elliptically outward in at least two or more regions. As a result, the flexible spline 22 of the gear system, in the two outward-deformed regions, have tooth engagements simultaneously with the two ring gears, that is, the circular spline 24 and the dynamic spline 26. In the regions of the short semiaxis of the elliptically deformed flexible spline, the flexible spline is not in tooth engagement with the circular spline 24 or the dynamic spline 26.
Upon rotation of the sun wheel 14 of the wave generator 12, the tooth engagement regions of the flexible spline 22 migrate with the angular position of the two planet wheels 16 of the wave generator, as shown in the different angular views in FIG. 3. The relative motion between the flexible spline 22 and the circular spline 24 results from the difference, for instance of two teeth, between the number of teeth of the flexible spline and of the circular spline. Upon one full revolution of the planet wheels 16 of the wave generator, the flexible spline 22 rotates relative to the circular spline 24 by the difference in the number of teeth between these two gear wheels. In the flat construction, the dynamic spline 26 serves as a driven element and has the same number of teeth as the flexible spline 22 and therefore also has the same speed and direction of rotation.
The use of a planetary gear system as the wave generator 12 offers the advantages, with a view to the degree of miniaturization of the micro gear system, that all the gear components can be produced with high precision using the known LIGA method described herein; the effort of assembly is reduced, since the wave generator comprises only three elements; the total transmission ratio of the gear is increased by the planetary gear system, so that by means of such a gear system, in a single stage, the very high speeds of rotation of micro motors can be adapted flexibly to individual requirements; and this variant of the wave generator 12 has very low moment of inertia, making highly dynamic positioning operations possible.